The invention relates to a thrust dynamic pressure bearing.
Conventionally, as shown in FIG. 2, a thrust dynamic pressure bearing is configured so that a flanged shaft 102 is inserted into a sleeve 101, and a flange-like plate 105 fixed to an end of the sleeve 101 and a step portion 101A of the sleeve 101 are opposed to a flange 103 of the shaft 102 with forming a predetermined dynamic pressure space S therebetween. The sleeve 101 and the plate 105 constitute a housing 100.
Dynamic pressure generating grooves 106 and 107 are formed in end faces of the flange 103, respectively. The space between the housing 101 and the flanged shaft 102 is filled with a dynamic pressure generating lubricant (not shown).
In the thrust dynamic pressure bearing, when the flanged shaft 102 relatively rotates with respect to the sleeve 101, the dynamic pressure generating grooves 106 and 107 formed in the flange 103 cause the dynamic pressure generating lubricant to generate a dynamic pressure, so as to support the shaft 102 with respect to the sleeve 101 in the thrust direction.
The prior art thrust dynamic pressure bearing involves the following problem. When the flange 103 is tilted with respect to the direction perpendicular to the axial center of the shaft 102, or when a force of tilting the shaft 102 with respect to the sleeve 101 is produced, an outer circumference portion 103A of the flange 103 comes into contact with the sleeve 101 and the plate 105, so as to cause some deficiency such as abrasion.
The thrust dynamic pressure bearing has another problem as follows. Even if the flange 103 is precisely perpendicular to the axial center of the shaft, the flange 103 unavoidably comes into contact with the sleeve 101 at starting and stopping. The dynamic pressure space S is easily clogged with abrasion powder generated by the contact.
Consequently, it is an object of the invention to provide a thrust dynamic pressure bearing in which an unsymmetrical contact during rotation is prevented from occurring, and a dynamic pressure space is prevented from being clogged with abrasion powder generated by a contact at starting and stopping.
In order to attain the object, the thrust dynamic pressure bearing of the invention of claim 1 is a thrust dynamic pressure bearing in which a thrust bearing face disposed on a housing is opposed to a thrust receiving face of a flange-like thrust receiving portion disposed on a shaft, at least one of the thrust bearing face and the thrust receiving face has dynamic pressure generating grooves for generating a dynamic pressure, and
a space between the thrust bearing face and the thrust receiving face is filled with a lubricant, and is characterized in that
the thrust receiving portion has a substantially tapered shape in section, a thickness of the thrust receiving portion becoming smaller as moving toward an outer circumference.
In the invention of claim 1, since the flange-like thrust receiving portion disposed on the shaft is tapered as moving toward the outer circumference thereof, the dynamic pressure space between the thrust bearing face of the housing and the thrust receiving face of the shaft during rotation becomes wider as moving toward the outer circumference thereof. According to the invention, even if the shaft is tilted with respect to the housing during rotation, therefore, it is possible to prevent an unsymmetrical contact of the thrust receiving face of the shaft in the vicinity of the outer circumference against the thrust bearing face of the housing, from occurring. In addition, since the dynamic pressure space becomes wider as moving toward the outer circumference, the abrasion powder generated by the contact at starting and stopping can be easily discharged from a radially inward portion toward a radially outward portion of the dynamic pressure space.
According to the invention, therefore, an unsymmetrical contact during rotation can be prevented from occurring, and the dynamic pressure space can be prevented from being clogged with the abrasion powder generated by the contact at starting and stopping. Consequently, a stable operation can be realized.
The thrust dynamic pressure bearing of the present invention is characterized in that a level difference between an innermost circumference end and an outermost circumference end of the thrust receiving portion is set in the range of 1 to 5 xcexcm.
In the present invention, since the level difference between the innermost circumference end and the outermost circumference end of the thrust receiving portion of the shaft is set in the range from 1 to 5 xcexcm, it is possible to prevent an unsymmetrical contact and the clog with the abrasion powder from occurring, while the dynamic pressure generating performance is sufficiently maintained.
If the level difference between the innermost circumference end and the outermost circumference end is set to be smaller than 1 xcexcm, it is difficult to prevent an unsymmetrical contact and the clog with the abrasion powder from occurring. If the level difference exceeds 5 xcexcm, the dynamic pressure generating performance is insufficient.